1. Field of the Invention
This invention is in the field of cardiology and methods therefor and, more particularly, is a system and method for detecting and locating heart disease, and especially coronary artery disease including myocardial ischaemia and infarction; however, the act of locating is with reference to myocardial ischemia and infarction.
2. Description of the Related Art
Coronary artery disease is the leading cause of death in the United States, yet the disease remains "silent" or dormant in the majority of patients until the fourth or fifth decade of life. At that point, coronary artery disease typically moves from the "silent" phase to a symptomatic phase, at which time the patient may experience as the first symptoms, angina pectoris, myocardial infarction, and/or sudden death.
The prevalence of coronary artery disease in the United States has been estimated as affecting over 4 million persons. Over 1 million are expected to suffer myocardial infarctions or sudden death before attaining the age of 60. Furthermore, once coronary artery disease is symptomatic--regardless of whether the symptoms comprise angina or myocardial infarction--the mortality rate is increased to 4% per year overall and 8% per year in those patients with an abnormal electrocardiogram or hypertension. This increased mortality rate is largely due to increases in the occurrence of sudden death, or the complications of repeated myocardial infarction.
Prior approaches to diagnose coronary artery disease fall into four general categories, which will be briefly discussed below. The first category falls under noninvasive, conventional EKG type tests, like the standard 12 lead EKG. Also, in this first category, some have practiced 24 hour ambulatory monitoring of the conventional EKG and stress test (see U.S. Pat. No. 3,267,934 to Thornton). This category of tests give ST segment depression and elevation readings as an indicator of myocardial ischaemia. However, ST segment changes are only sensitive to some portion of coronary artery diseases. Accordingly, tests such as these have limited value for the diagnosis of coronary artery disease, as they are relatively insensitive in detection of certain potential events. A second group of approaches to detect coronary artery disease involves more expensive noninvasive tests, such as nuclear imaging. Also, this cluster of approaches may involve an invasive assessment of cardiac catheterization and coronary angiography. This second group of tests has the disadvantage of being expensive and/or invasive.
A third approach to the detection of coronary artery disease involves the use of software programs to analyze conventional EKGs. One such approach is the cardiointegram (CIG) which applies a process of integration over various sections of the QRST signal. The High Frequency Electrocardiogram (HFECG) is another software-based method which derives high frequency components of the EKG following a fast-Fourier transformation. The methods of this third group of approaches are either performed on every single heart beat or on the averaged QRS complex. When analyzing single heart beats, much potentially meaningful information is simply not evaluated. On the other hand, techniques based on analyzing a single averaged QRS complex seem to be able to distinguish minor signal changes from noise, but there are significant limitations to these types of methods as well. For example, the averaged EKG is based on the QRS superimposition, and the precision of superimposition is limited by sample rate, QRS identification software, analytical experience of the user, and heart rate variability. Accordingly, use of this third group of analysis techniques is also limited in terms of effectiveness at fully and accurately detecting coronary artery disease.
A fourth technique is exemplified by an article entitled "The Theoretical Basis and Clinical Study of EKG Multiphase Information (EMPI) System" (for The American Society of Hypertension, Sixth Scientific Meeting by Dan Qun Fang et al.), and by U.S. Pat. No. 5,509,425, entitled "Arrangement for and Method of Diagnosing and Warning of a Heart Attack." In this approach, power spectrum and other frequency domain analyses are used to extract additional information from a conventional EKG; however, this technique also has its shortcomings. Specifically, Fourier transformation of the time domain signals into the frequency domain is conducted on only two EKG leads, namely lead V5 and lead II, thereby unnecessarily forfeiting the very potentially beneficial analyses of the remaining EKG leads. Additionally, this approach failed to establish use of a base value (as set forth in the current invention) in its analysis of power spectrum signals.
Therefore, there existed a need to provide a system and method for improved detection of coronary artery and heart disease. Moreover, the instant invention provides a system and method for not only detecting coronary artery and heart disease, but also locating such ailments, when detected.